In the related art, there is an air-conditioning apparatus for heat transport in which a refrigeration cycle is constituted by connecting a compressor, a heat source side heat exchanger, an expansion valve, and an intermediate heat exchanger in sequence via pipes, and in which a pump, a use side heat exchanger, and the intermediate heat exchanger are connected in series, thereby performing heat transport so as to transport cooling energy and heating energy generated in the refrigeration cycle to the use side heat exchanger using a heat medium such as water or brine (for example, see Patent Literatures 1 to 3). The air-conditioning apparatus as described above has an advantage in that the amount of refrigerant enclosed therein can be reduced in comparison with a normal direct expansion air conditioner. Also, in a normal air-conditioning apparatus, if refrigerant leaks indoors, the refrigerant can have adverse effects on the human body due to its toxicity, combustibility, and the like, whereas in the air-conditioning apparatus described above, there is no risk of any indoor leak because no refrigerant piping is provided indoors.
In an air-conditioning apparatus described in Patent Literature 1, stable air conditioning is achieved by controlling the flow rate of heat source water flowing into a water heat exchanger in association with the fluctuations in the inlet water temperature of the heat source water. In this air-conditioning apparatus (cold/hot water coil air conditioner), the temperature of the heat source water is controlled to change on the order of 5 degrees C. for both a cooling operation and a heating operation. For example, the temperature of the heat source water is changed from 7-10 degrees C. to 12-15 degrees C. during the cooling operation, and the temperature of the heat source water is changed from 40-45 degrees C. to 35-40 degrees C. during the heating operation.
Also, an air-conditioning apparatus described in Patent Literature 2 generates a counter flow of fluids (for example, refrigerant, water, air, and the like) passing through a main (water) heat exchanger or a use side (indoor) heat exchanger and sets the difference between the inlet and outlet temperatures of water to be 10 degrees C. or larger, thereby achieving reduction of the size of the air-conditioning unit and reduction of the transport energy. In addition, an air-conditioning apparatus described in Patent Literature 3 measures electrical inputs of a compressor and a pump and controls the operation of the pump on the basis of a rotation speed when the sum of the electrical inputs of the compressor and the pump becomes small.